An apparatus that has an actuator such as a hydraulic pressure cylinder has a filtration device in order to filter liquid, such as hydraulic and/or transmission oil, that circulates in a hydraulic pressurized circuit. The filtration device has a housing and a filter element in the housing which filters hydraulic and/or transmission fluid.
The filtration device is equipped with a vent valve apparatus that vents air that is trapped within the housing depressurizing and forcing air to the outside of the housing.
The vent valve apparatus is installed directly in the housing, and vents air that is trapped in between the housing and the filter element.
If the filter element has filtration material in the shape of, for instance, a tube and filters hydraulic oil when the oil passes the filtration material (filter media) between the inner side and outer side thereof, the filtration material will also be trapped inside the filter element.
Furthermore, in this type of filtration device, air may be trapped both in the gap between the filter element and the housing and inside the filter element.
However, while the vent valve apparatus of the aforementioned type can vent the air that is trapped in the space defined between the housing and the filtration material, air trapped inside the filter element will not be vented.
Furthermore, when exchanging the filter element, before the housing is opened, the hydraulic oil that remains within the housing is drained, via a drain valve. When this occurs, air flows into the housing by opening the vent valve, which in turn causes the hydraulic liquid to flow out of the filter housing.
However, if the filter element is tubular, it is difficult for air to flow into the inside of the filter element due to the filter material's resistance. Consequently, it is difficult to drain the hydraulic oil that remains inside the filter element.
Therefore, one objective of this invention is to provide a filtration device that vents air trapped inside the filter element and efficiently drains liquid from the inside of the filter element.